Muscarinic cholinergic and beta-adrenergic neuronal characteristics in fibroblasts continue to be investigated and applied to clinical issues. Cholinergic characteristics identified in fibroblasts include choline acetyl transferase activity and high affinity choline uptake. Muscarinic receptors on fibroblasts have increased density after atropine incubation, which returns to normal after atropine is removed. Cholinergic agonists produce inhibition of norepinephrine-stimulated adenyl cyclase. Beta-adrenergic receptors on fibroblasts have significantly reduced density in patients with affective illness and ill relatives, which in combination with our previous finding of decreased muscarinic receptor density in these individuals, supports the cholinergic-adrenergic balance hypothesis of affective disorders. Analysis of family and linkage data in pedigrees shows single locus control of platelet MAO activity. A family study of schizophrenia has been undertaken. In the recombinant DNA laboratory, a restriction fragment lengths polymorphism of proopiomelanocartin (POMC) has been identified.